Fluoride & IQ: The 53 Studies

As of June 2018, a total of 60 studies have investigated the relationship between fluoride and human intelligence, and over 40 studies have investigated the relationship fluoride and learning/memory in animals. Of these investigations, 53 studies have found that elevated fluoride exposure is associated with reduced IQ in humans, while 45 animal studies have found that fluoride exposure impairs the learning and/or memory capacity of animals. The human studies, which are based on IQ examinations of over 15,000 children, provide compelling evidence that fluoride exposure during the early years of life can damage a child’s developing brain.

After reviewing 27 of the human IQ studies, a team of Harvard scientists concluded that fluoride’s effect on the young brain should now be a “high research priority.” (Choi, et al 2012). Other reviewers have reached similar conclusions, including the prestigious National Research Council (NRC), and scientists in the Neurotoxicology Division of the Environmental Protection Agency (Mundy, et al). In the table below, we summarize the results from the 51 studies that have found associations between fluoride and reduced IQ and provide links to full-text copies of the studies. For a discussion of the 7 studies that did not find an association between fluoride and IQ, click here.

Fluoride Levels in Urine: About a quarter of the IQ studies have provided data on the level of fluoride in the children’s urine, with the majority of these studies reporting that the average urine fluoride level was below 3 mg/L. To put this level in perspective, a study from England found that 5.6% of the adult population in fluoridated areas have urinary fluoride levels exceeding 3 mg/L, and 1.1% have levels exceeding 4 mg/L. (Mansfield 1999) Although there is an appalling absence of urinary fluoride data among children in the United States, the excess ingestion of fluoride toothpaste among some young children is almost certain to produce urinary fluoride levels that exceed 2 ppm in a portion of the child population.

In-Utero Exposure:Bashash 2017 and Valdez Jiménez 2017 evaluated the association of in utero exposure to fluoride on the offspring. The determination of the fluoride exposure was through urine analysis during the pregnancy.

Methodological Limitations

As both the NRC and Harvard reviews have correctly pointed out, many of the fluoride/IQ studies have used relatively simple designs and have failed to adequately control for all of the factors that can impact a child’s intelligence (e.g., parental education, socioeconomic status, lead and arsenic exposure). For several reasons, however, it isunlikely that these limitations can explain the association between fluoride and IQ.

First, some of the fluoride/IQ studies have controlled for the key relevant factors, and significant associations between fluoride and reduced IQ were still observed. This fact was confirmed in the Harvard review, which reported that the association between fluoride and IQ remains significant when considering only those studies that controlled for certain key factors (e.g., arsenic, iodine, etc). Indeed, the two studies that controlled for the largest number of factors (Rocha Amador 2007; Xiang 2003a,b) reported some of the largest associations between fluoride and IQ to date.

Second, the association between fluoride and reduced IQ in children is predicted by, and entirely consistent with, a large body of other evidence. Other human studies, for example, have found associations between fluoride, cognition, and neurobehavior in ways consistent with fluoride being a neurotoxin. In addition, animal studies have repeatedly found that fluoride impairs the learning and memory capacity of rats under carefully controlled laboratory conditions. An even larger body of animal research has found that fluoride can directly damage the brain, a finding that has been confirmed in studies of aborted human fetuses from high-fluoride areas.

Finally, it is worth considering that before any of the studies finding reduced IQ in humans were known in the western world, a team of U.S. scientists at a Harvard-affiliated research center predicted (based on behavioral effects they observed in fluoride-treated animals) that fluoride might be capable of reducing IQ in humans. (Mullenix 1995)

Summary

When considering their consistency with numerous animal studies, it is very unlikely that the 53 human studies finding associations between fluoride and reduced IQ can all be a random fluke. The question today, therefore, is less whether fluoride reduces IQ, but at what dose, at what time, and how this dose and time varies based on an individual’s nutritional status, health status, and exposure to other contaminants (e.g., aluminum, arsenic, lead, etc). Of particular concern is fluoride’s effect on children born to women with suboptimal iodine intake during the time of pregnancy, and/or fluoride’s effects on infants and toddlers with suboptimal iodine intake themselves. According to the U.S. Centers for Disease Control, approximately 12% of the U.S. population has deficient exposure to iodine.

The water fluoride concentration ranged from 0.20 mg/L to 1.00 mg/L, with a mean value of 0.50 ± 0.27 mg/L in the normal fluoride exposure group, and from 1.10 mg/L to 3.90 mg/L, with a mean value of 2.00 ± 0.75 mg/L in the high-fluoride exposure group (Table 1).

Type of IQ Test:

We examined the dose-response effects of low-to-moderate fluorideexposure on dentalfluorosis (DF) and intelligence quotient (IQ), and evaluated the potential relationships between DF grades and intelligence levels using piecewise linear regression and multiple logistic regression, respectively.IQ scores were measured using the second edition of Combined Raven’s Test–The Rural in China (CRT-RC2) (Liu et al., 2009) for children aged 7 to 13 years. The CRT-RC2 is a validated test for basic cognitive abilities, and has been widely adopted in China after modifications, as it is non-verbal and less affected by language, and cultural and ethnic differences (Sun et al., 2015).

Dean’s fluorosis index (WHO criteria) (Molina-Frechero et al., 2015) was used to estimate the prevalence and severity of DF. Each participant was examined by two qualified and independent experts, who had rich experience on examination of dental fluorosis… The final diagnosis was made only when judgments from the two experts were in agreement; if not, a third expert would join in and offer suggestion. For repeatability, 10% of participants were double checked and the Kappa value was 0.82.

Results:

The adjusted odds ratios (ORs) of DF were 2.24 (95% confidence interval [CI]: 2.02 to 2.48) for every 0.1 mg/L increment in the water fluoride concentration in the range of 0.80 to 1.50 mg/L, and 2.61 (95% CI: 2.32 to 2.93) for every 0.5 mg/L increment in the urinary fluoride level up to 1.80 mg/L. Every 0.5 mg/L increment in the water fluoride level was associated with a reduction of 4.29 in the IQ score (95% CI: -8.09 to -0.48) in the range of 3.40 to 3.90 mg/L, and a decreased probability of developing excellentintelligence (IQ ?130, OR = 0.60, 95% CI: 0.47 to 0.77) in the range of 0.20-1.40 mg/L, respectively. Every 0.5 mg/L increment in the urinary fluoride level was related to a decrease of 2.67 in the IQ scores (95% CI: -4.67 to -0.68) between 1.60 mg/L to 2.50 mg/L. Excellentintelligence decreased by 51% in children with higher urinary fluoride, and by 30% with each degree increment of DF.

Conclusions:

In conclusion, chronic exposure to excessive fluoride, even at a moderate level, was inversely associated with children’s dental health and intelligence scores, especially excellent intelligence performance, with threshold and saturation effects observed in the dose-response relationships. Additionally, DF severity is positively associated with the loss of high intelligence, and may be useful for the identification of individuals with the loss of excellent intelligence. Thus, it is important to monitor water quality, and supply fluoride-free drinking water to safeguard children’s health.

Natural water fluoride levels in Mexico City may range from 0.15 to 1.38 mg/L

Type of IQ Test:

“At age 4 y, neurocognitive outcomes were measured using a standardized version of McCarthy Scales of Children’s Abilities. For children 6–12 y old a Spanish-version of the Wechsler Abbreviated Scale of Intelligence.”

“In this study, higher prenatal fluoride exposure, in the general range of exposures reported for other general population samples of pregnant women and nonpregnant adults, was associated with lower scores on tests of cognitive function in the offspring at age 4 and 6–12 y.”

Durango City and Lagos de Moreno, Jalisco, Mexico. Both are endemic hydro-fluorosis areas.

Size of Study:

“65 mother-infant pairs recruited from 2013 to 2014. Inclusion criteria were: 12 weeks of gestation, with no history of thyroid disease, without clinically diagnosed diabetes, and a minimum 5 years of residence in the study area.”

Age of Subjects:

“The average age of children assessed was 8 months (3–15 months) and almost 70% were girls.” The average age of the mothers was 22.4 ±4.0.

Source of Fluoride:

The study was performed in an endemic hydrofuorosis area. According to the authors: ‘in Mexico F in water remains as the main source of F exposure. In endemic hydrofuorosis areas of Mexico only non-fluorinated salt is distributed according to the NOM-040-SSA1-1993.”

Water Fluoride Level:

F levels in tap water mean concentrations for each trimester were: 2.6 ±1.1 mg/l, 3.1 ±1.1 mg/l and 3.7 ±1.0 mg/l respectively. It is worthy to note that over 81.5% of the samples of tap water were above 1.5 mg/l (NOM-127- SSA1-1994) with the highest value of 12.5 mg/.

33.8% of women reported drink tap water and 78.4% use it for cooking. The practice of use tap water for drink or cooking is crucial because exposure to F could be increased when the infant change to bottle feeding and starts solid foods. Regarding, bottled water it is important to mention that we have analyzed several brands of this water and 65% of the samples exceeded the 0.7 mg/l value (NOM-041-SSA1-1993) and 22.9% had values over 1.5 mg/l (NOM-127-SSA1-1994) data not shown.

Type of IQ Test:

“Neurodevelopment was assessed with the Bayley Scales of Infant Development II (BSDI-II) (Bayley, 1993). This test has good reliability and validity; it is applied to evaluate developmental delay in children between 3 months to 5 years in Mexico by the SSA (CNPSS, 2013). The Mental Development Index scale (MDI) of the Bayley test evaluate aspects of functioning such as eye-hand coordination, manipulation, understanding of object relation, imitation and early language development whereas the Psycho-motor Development Index (PDI) scale assesses gross motor development… To standardize the raw scores for children who were born prematurely, the number of months of prematurity was subtracted from their chronological age. The scores below 85 points indicated a possible developmental delay.”

Results:

In this study near to 60% of the children consumed contaminated water and the prevalence of children with IQ below 90 points was 25% in the control group (F urine 1.5 mg/g creatinine) in comparison with the 58% of children in the exposed group (F urine >5 mg/g creatinine) (OR = 4.1, CI 95% 1.3–13.2) (data unpublished).

Only 66.2% of the babies were at term. “We found higher levels of F in urine across trimester in premature compared with full term 2.4 vs 1.6 mg/l (1st); 2.3 vs 1.8 mg/l (2nd); and 4.1 vs 2.8 mg/l (3rd) (data not shown)

Conclusions:

“After adjusting for potential confounding factors (gestational age, age of child, marginalization index and type of water for consumption), the MDI [Mental Development Index] showed an inverse association with F levels in maternal urine for the first (b = -19.05, p = 0.04) and second trimester (b = -19.34, p = 0.01). Our data suggests that cognitive alterations in children born from exposed mothers to F could start in early prenatal stages of life.

“IQ has anegative significant correlation with dental fluorosis (r=0.253,P<0.01). Dental fluorosis acts as an indicator of decreasing level of IQ. As fluorosis is a consequence of fluoride exposure, so IQ has a negative significant correlation with exposure dose (r =0.343, P<0.01) which was considered as a fluoride input source.”

“IQ values were plotted against the urinary fluoride concentration and it was found that they have a significant negative correlation (r=0.751, P<0.01).”

Conclusion

“[C]hildren residing in areas with higher than normal water fluoride level demonstrated more impaired development of intelligence and moderate [dental fluorosis]. Millions of children including adults around the world are affected by higher level of fluoride concentration through their drinking water and are therefore potentially at risk. It is concluded that for the benefit of the future generation, urgent attention should be paid on this substantial public health problem.”

“Mean F concentration in the study area varies from 0.32 to 13.29 mg/L.”

Type of IQ Test:

Raven Standard Theoretical Intelligence Test

Results:

“This study indicates that students exposed to high F (children of Junidpur and Nowapara) show an average IQ of 21.17 ± 6.77 in comparison with low-F exposed students (children of Bilaspur, Mohula, Bhalian) having an average IQ of 26.41 ± 10.46. . . . Statistical analysis (Z test) demonstrates that there is a significant (Z = 2.59) difference in IQ among the high- and low-F area student.”

Conclusion

“[S]tudents of the study area have less IQ than students of non-contaminated area, demonstrating that consumption of F also has a major role with the intellectual development of
children.”

Khan SA, et al. (2015). Relationship between dental fluorosis and intelligence quotient of school going children in and around Lucknow district: a cross-sectional study. Journal of Clinical & Diagnostic Research9(11):ZC10-15.

Location of Study:

Lucknow district, India.

Size of Study:

429 schoolchildren

Age of Subjects:

6-12 years old

Source of Fluoride:

Water

Results:

“In this study, on comparison of children at two locations according to IQ grades [Table/Fig-4], majority of the children (74.8%) living in low fluoride area had an IQ grade 2 (definitely above the average in intellectual capacity). None of the children from the low fluoride area had an IQ grade 4 and 5 (definitely below average and intellectually impaired). On the other hand, majority of children (58.1%) from high fluoride area fall under IQ grade 3 (intellectually average). None of the children from high fluoride area had an IQ grade 1 (intellectually superior). This difference in IQ grades of children amongst the two areas was found to be statistically significant (p<0.001).””[I]t is clearly evident that with increase in the grade of fluorosis, a trend of increase in the IQ grade (decrease in intellectual capacity) was observed indicating a strong correlation between fluorosis grade and IQ grade (Spearman’s p=0.766).”

Conclusion:

“The data from this research may support the hypothesis that excess fluoride in drinking water has toxic effects on the nervous system.”

Sebastian ST, Sunitha S. 2015. A cross-sectional study to assess the intelligence quotient (IQ) of school going children aged 10-12 years in villages of Mysore district, India with different fluoride levels. Journal of the Indian Society of Pedodontics and Preventive Dentistry 33(4):307-11.

Location of Study:

Mysore district, India

Size of Study:

405 schoolchildren (135 children from high fluoride area; 135 children from “normal” fluoride area; 135 chidren from “low” fluoride area)

“In bivariate analysis, significant relationships were found between water fluoride levels and Intelligence Quotient of school children (P < 0.05). In the high fluoride village, the proportion of children with IQ below 90, i.e. below average IQ was larger compared to normal and low fluoride village. Age, gender, parent education level and family income had no significant association with IQ.”

Conclusion:

“School children residing in area with higher than normal water fluoride level demonstrated more impaired development of intelligence when compared to school children residing in areas with normal and low water fluoride levels.”

Kundu H, et al. (2015). Effect of fluoride in drinking water on children’s intelligence in high and low fluoride areas of Delhi. Journal of the Indian Association of Public Health Dentistry 13(2):116-121. April-June.

Location of Study:

Delhi, India.

Size of Study:

200 school children: 100 from low F area and 100 from high F area.

Age of Subjects:

8-12 years of age.

Equal numbers of male and female children were included in the study.

Source of Fluoride:

Water

Type of Cognitive Tests:

Ravens Standardized Progressive Matrices Test

Results:

“Comparison of mean IQ of children in both high (76.20 ± 19.10) and low F (85.80 ± 18.85) areas showed a significant difference (P = 0.013). Multiple regression analysis between child IQ and all other independent variables revealed that mother’s diet during pregnancy (P = 0.001) along with F in drinking water (P = 0.017) were the independent variables with the greatest explanatory power for child IQ variance (r2 = 0.417) without interaction with other variables.”

Conclusion:

“Fluoride in the drinking water was significantly related with the IQ of children. Along with fluoride, mother’s diet during pregnancy was also found to be significantly related with IQ of children.”

“In this rural community, social differences are limited. The parents or guardians completed a questionnaire on demographic and personal characteristics including the child’s sex, age at testing, parity, illnesses before age 3, past medical history of the child and caretakers, parental or guardian age, education and occupational histories, and residential history, and household income. It is known that iron deficiency can impair motor and mental developments in children, iron concentration was therefore considered as a covariate. These potential confounders were used for adjustment in the statistical analysis.”

“Among possible confounders, both arsenic and lead are known to be low in drinking water in the area.”

Type of Cognitive Tests:

WRAML, WISC-R, WRAVMA

Results:

“Results of our pilot study showed that moderate and severe dental fluorosis was significantly associated with deficits in WISC-R digit span. Children with moderate or severe dental fluorosis scored significantly lower in total and backward digit span tests than thosewith normal or questionable fluorosis. These results suggest a deficit in working memory. Scores on other tests did not show significant relationships with indices of fluoride exposure.”

Conclusion:

“Results of our field study raise a concern about the safety of elevated systemic exposure to fluoride from high concentrations in the drinking water.While topical fluoride treatment confers benefits of reducing caries incidence, the systemic exposure should not be so high as to impair children’s neurodevelopment especially during the highly vulnerable windows of brain development in utero and during infancy and childhood and may result in permanent brain injury. We are planning a larger scale study to better understand the dose–effect relationships for fluoride’s developmental neurotoxicity in order to characterize the appropriate means of avoiding neurotoxic risks while securing oral health benefits.”

“Covariates included the indicator variables for age, gender, educational levels of parents (primary and below, junior high school, senior high school, and above), and continuous variables for drinking water fluoride (mg/l) and levels of thyroid hormones (T3, T4, and TSH).”

Results:

“[T]he present work demonstrated that the IQ scores of children exposed to high fluoride drinking water were significantly lower than those who lived in control area . . . . [O]ur findings further showed that, across the full range of serum and urinary fluoride, children’s IQ decreased gradually with the increase of fluoride contents in serum and urine, in a dose-dependent manner.”

Conclusion:

“In summary, our data suggest that the intelligence of children is affected by the COMT gene polymorphism and, in particular, this SNP plays a role in modifying the effect of fluoride exposure on cognition. Children with COMT reference allele had a higher risk for cognitive impairments after fluoride exposure. Additionally, proteomics analysis represents early specific markers of developmental fluoride neurotoxicity. Hence, our findings provide certain basis for clarifying the mechanisms and identifying molecular targets of pharmacological interventions for potential delayed therapy.”

Bai Z, et al. (2014) Investigation and analysis of the development of intelligence levels and growth of children in areas suffering fluorine and arsenic toxicity from pollution from burning coal. Chinese Journal of Endemiology 33(2):160-163.

Location of Study:

Shaanxi Province, China.

Size of Study:

303 children (120 children from high-fluoride area; 95 from mid-fluoride area, 98 from low-fluoride area)

Age of Subjects:

8 to 12 years old

Source of Fluoride

Coal burning

Urine Fluoride Levels:

“The median urinary fluoride levels for children 8–12 years old in the areas of significant, minor and no morbidity were, respectively, 1.96, 0.81 and 0.54 mg/L.”

Wei N, et al. (2014). The effects of comprehensive control measures on intelligence of school-age children in coal-burning-borne endemic fluorosis areas. Chinese Journal of Endemiology 33(3):320-22.

Location of Study:

Bijie City, Guizhou Provinc, China.

Size of Study:

741 children (104 children from low-fluoride area; 298 children from an endemic fluorosis area with long-term defluoridation measures; 339 children from endemic fluorosis area with short-term defluoridation measures).

“Above average IQ of children in the control group was 97.1% (101/104),which was significantly higher than that of long and short treatment groups; after a lengthy treatment, mental retardation detection rate was significantly lower in the low-age group,8-10 year-old children(x2 =7.542,P < 0.01). Urinary fluoride content was negatively correlated with the level of IQ (r =-0.553,P < 0.01).“

Conclusion:

“The intelligence development of children in coal-burning-borne endemic fluorosis area is significantly delayed. After a certain period of comprehensive treatment,the decreased level of cognition is inhibited and the mental retardation in the low-age group is improved.”

Nagarajappa R, et al. (2013). Comparative assessment of intelligence quotient among children living in high and low fluoride areas of Kutch, India: a pilot study. Iranian Journal of Public Health2(8): 813–818.

Location of Study:

Kutch District, Gujarat, India

Size of Study:

100 children (50 children from high-fluoride area; 50 children from control area)

Age of Subjects:

8-10 years old

Source of Fluoride:

Water

Water Fluoride Levels:

High Fluoride: 2.4 to 3.5 mg/L; Control: 0.5mg/L.

Type of IQ Test:

Seguin Form Board Test

Results:

“Mean scores for average, shortest and total timing category were found to be significantly higher (P<0.05) among children living in Mundra (30.45±4.97) than those living in Bhuj (23.20±6.21). Mean differences at 95% confidence interval for these timings were found to be 7.24, 7.28 and 21.78 respectively.”

Conclusion:

“Chronic exposure to high levels of fluoride in water was observed to be associated with lower intelligence quotient.”

Karimzade S, et al. (2014). Investigation of intelligence quotient in 9-12-year-old children exposed to high- and low-drinking water fluoride in West Azerbaijan province, Iran. Fluoride 47(1):9-14.

Location of Study:

Poldashi and Piranshahr, West Azerbaijan province, Iran.

Size of Study:

39 male children (19 from high-fluoride area; 20 from control area)

Age of Subjects:

9 to 12 year olds

Source of Fluoride:

Water

Water Fluoride Levels:

High Fluoride = 3.94 mg/L
Control = 0.25 mg/L

Confounding Factors:

No significant differences were found in the potential confounding factors of educational, economic, social, cultural, and general demographic characteristics between the high- and low-F regions.

Type of IQ Test:

Iranian version of the Raymond B Cattell test

Results:

“The IQ of the 19 children in the high-F region was lower (mean±SD: 81.21±16.17), than that of the 20 children in the low-F region (mean±SD: 104.25±20.73, p=0.0004). In the high-F region, 57.8% had scores indicating mental retardation (IQ <70) or borderline intelligence (IQ 70–79), while this figure was only 10% in the low–F region.”

Conclusions:

“The study found that children residing in a region with a high drinking water F level had lower IQs compared to children living in a low drinking water F region (p<0.001). The differences could not be attributed to confounding educational, economic, social, cultural, and general demographic factors.”

Trivedi MH, et al. (2012). Assessment of groundwater quality with special reference to fluoride and its impact on IQ of schoolchildren in six villages of the Mundra Region, Kachchh, Gujurat, India. Fluoride 45(4):377-83.

Location of Study:

Gujurat, India

Size of Study:

84 children (34 from high-fluoride villages, 50 children from control village)

Age of Subjects:

6th and 7th grade students

Source of Fluoride:

Water

Water Fluoride Levels:

High Fluoride = 2.3 + 0.87 mg/L
Control = 0.83 + 0.38 mg/L

Urine Fluoride Levels:

High Fluoride = 2.69 + 0.92 mg/L
Control = 0.42 + 0.23

Confounding Factors:

Same socioeconomic status (E on an A-E scale); same attendance status at school (regular students attending more than 80% of classes)

Type of IQ Test:

Questionnaire prepared by Prof. JH Shah; standardized on the Gujarati population with 97% reliability rate in relation to the Stanford-Binet Intelligence Scale

Results:

“The average IQ score of the 34 students drinking the high F water was significantly lower (p?0.05) than among the 50 students drinking the low F water.”

Conclusions:

“the present investigation concludes that the three villages of Chhasara, Gundala, and Mundra, are F-contaminated villages. Because of high F concentrations in the [groundwater], children in these villages have greater exposure to F that may lead in to low IQ as compared to the nearby villages of Baroi, Zarpara, and Pragpar, which have low F in their [groundwater].”

(1) No significant differences in urinary lead, arsenic, or iodine levels between the four groups. (2) No significant differences in gender ratio, socio-economic status, SES, parental education, height/age ratio, and weight/height ratio. (3) Children were excluded if they were not lifelong resident of area, if they had changed their water source since birth, or if they had history of congenital or acquired neurological disease and/or head injury.

IQ Test:

Raven’s Standard Progressive Matrices

Results:

“Reduction in intelligence was observed with an increased water fluoride level (P 0.000). The urinary fluoride level was a significant predictor for intelligence (P 0.000).”

Conclusion:

“This study indicates that exposure to fluoride is associated with reduced intelligence in children. We have found a significant inverse relationship between intelligence and the water fluoride level, and intelligence and the urinary fluoride level. After adjusting for confounders, urinary fluoride was the significant predictor for intelligence.”

(1) Sites selected to match social and natural factors like economic situation, educational standard, and geological environments. (2) Schools had similar teaching quality. (3) Sites are not exposed to known neurotoxins (e.g. arsenic) in drinking water, nor are they endemic areas for iodine deficiency disorders. (4) Five children who had not lived in these areas at least 1 year were excluded.

IQ Test:

CRT-RC3 (Combined Raven’s Test for Rural China)

Results:

Children’s IQ was inversely related to urinary fluoride content, (p<0.0001). Each increase in 1 mg/L of urine F was associated with 0.59 point decrease in IQ (p=0.0226).

Conclusion:

“In conclusion, our study suggested that low levels of fluoride exposure in drinking water had negative effects on children’s intelligence and dental health and confirmed the dose-response relationships between urine fluoride and IQ scores as well as dental fluorosis.”

(1) Children included were continuous residents of study villages since birth; drinking water from same public water supply (1 per village); (2) attended same high school (1 per village). (3) Children with history of trauma or injury to head; affected by congenital or acquired neurological disorders, psychological disorders were excluded.

Type of IQ Test

Raven’s Standard Progressive Matrices Test

Results:

63.2% of children in high F area had IQ less than 90, versus 47.7% of children in low F village. (p=0.06).

Conclusion:

“Though there was a trend in our study towards lower IQ in a greater number of children from high F village than in the low F village, probably the small sample size of the present study failed to establish a statistically significant difference.”

(1) Children included in study had normal birth history, were permanent residents in the region of study, had no history of trauma to the head, no history of chronic illness, not on medication. (2) Villages have similar culture, standard of living, and lifestyle habits.

Type of IQ Test

Raven’s Colored Progressive Matrices Test

Results:

(A) Children with dental fluorosis had lower IQ (66.63+18.09) than those without dental fluorosis (76.36+20.84), p < 0.05. (B) Children with mild dental fluorosis had lower IQ (66.73) than those without dental fluorosis (75.89), p < 0.05.

Conclusion:

“Previous studies had indicated toward decreased Intelligence in children exposed to high levels of fluoride and our study also confirmed such an effect.”

Sudhir KM, et al. (2009). Effect of fluoride exposure on intelligence quotient (IQ) among 13-15 year old school children of known endemic area of fluorosis, Nalgonda District, Andhra Pradesh. Journal of the Indian Association of Public Health Dentistry 13:88-94.

(1) All children were born and raised in the respective areas. (2) Children were excluded if they had been diagnosed with physical deformation, developmental disorders, delayed mental development, emotional/behavioral obstacles or challenges, or other forms of mental disorders.

Type of IQ Test

CRT-RC (Combined Raven’s Test for Rural China)

Results:

– IQ decreased with increasing F level in urine (p < 0.01) – IQ was significantly reduced among children with severe fluorosis as compared to children without fluorosis (p < 0.05) – A trend (albeit not statistically significant) for IQ to decrease with increasing severity of dental fluorosis (NS) and with increasing severity of the region’s fluoride poisoning

Conclusion:

“High exposure to fluoride most definitely has an adverse effect on the development of intelligence in children, in particular on the capability of abstract inference.”

(1) A multiple regression analysis was used that controlled for blood lead levels, socioeconomic status, mother’s education, height-for-age (an index of malnutrition), and transferrin saturation. (2) Each child’s water fluoride level, and urine fluoride level, levels were individually determined. (3) The test examiner was blinded as to the children’s fluoride exposure.

(1) Both fluoride in urine, and fluoride in water, were significantly correlated with IQ, and this correlation remained significant after controlling for lead exposure, socioeconomic status, mother’s education, malnutrition, and transferrin. (2) Fluoride’s effect on IQ was larger than the effect from arsenic.

Conclusion:

“We found that exposure to F in urine was associated with reduced Performance, Verbal and Full IQ scores before and after adjusting for confounders. The same pattern was observed for models with F in water as the exposure variable. . . . The individual effect of F in urine indicated that for each mg increase of F in urine a decrease of 1.7 points in Full IQ might be expected.”

(1) Arsenic used as variable. Similar manganese levels in water for all groups. (2) All groups lived in rural areas with similar geographic and cultural conditions and a comparable level of socioeconomic development (years of parental education, average income, years of exposure). (3) All children currently attending school.

Type of IQ Test

CRT-RC (Combined Raven’s Test for Rural China)

Results:

– Average IQ in high-arsenic area (95.1+16.6) is significantly lower than IQ in control area (104.8+14.7). p < 0.05 – The average IQ in high-fluoride area (100.5+15.8) is also significantly lower than average IQ in control area (104.8+14.7). p < 0.05 – Significantly more children with IQ lower than 70 (mental retardation) in high-F area (4%), medium-arsenic area (3.3%), and high-arsenic area (8.3%) as compared to control (0%).

Conclusion:

“This study indicates that exposure to fluoride in drinking water is associated with neurotoxic effects in children.”

(1) The study included only those children who were life-long residents of the areas. respective location. (2) The areas have similar nutritional status and both have middle class socioeconomic status (although Sachana is slightly poorer). (3) Iodized salt is used in both areas.

Type of IQ Test

Questionnaire prepared by Prof. JH Shah; standardized on the Gujarati population with 97% reliability rate in relation to the Stanford-Binet Intelligence Scale

Results:

(A) Average IQ is lower in High-F area (91.72+1.13) than in Low-F area (104.44+1.23), p<0.001. (B) High F area has 28.09% of children with IQ below normal (over twice the percentage found in lower F area).

Conclusion:

“In agreement with other studies elsewhere, these findings indicate that children drinking high F water are at risk for impaired development of intelligence.”

(1) The two areas have common habits and lifestyles in terms of cuisine, economy, culture, education, agricultural goods, etc.. (2) No chemical factories in area. (3) The area does not have an iodine deficiency problem.

Type of IQ Test

CRT-C2 intelligence module

Results:

(A) Average IQ in High-F area (96.11 + 12.00) is lower than Low-F area (98.41 + 14.75), although difference is not statistically significant. (B) No child in High-F area has outstanding or excellent intelligence. The respective rates in the Low-F area are 2.7% and 5.4%, respectively.

Conclusion:

“Exposure to high levels of fluoride is likely to cause a certain level of harm to a child’s level of intelligence.”

126 children (85 children from low-F village, 41 children from high-F village)

Age of Subjects:

Not provided in English abstract (full study is in Persian)

Source of Fluoride:

Water

Water Fluoride Levels:

High F village = 2.5 mg/L
Low F village = 0.4 mg/L

Confounding Factors:

The history of illnesses affecting the nervous system, head trauma, birth weight (>2.5kg or < 2.5kg), residental history, age and sex of children were investigated by questionnaires completed by the children’s parents.

Type of IQ Test

Raven’s

Results:

“In the high fluoride area the mean IQ of children (87.9±11) was significantly lower than in the low fluoride area (98.9±12.9) (P=0.025).”

Statistical significance

““Based on the findings of this study, exposure of children to high levels of fluoride may carry the risk of impaired development of intelligence.”

512 children (222 children in high-F village, 290 children in low-F village)

Age of Subjects:

8-13 years old

Type of Exposure:

Water

Water Fluoride Levels:

High F village=2.47+0.79 mg/L (range=0.57-4.50 mg/L)
Low F village=0.36+0.15 mg/L (range=0.18-0.76 mg/L)In the high-F village, children were subdivided into the following five fluoride water levels:Group A<1.0 mg/L;
Group B=1.0-1.9 mg/L;
Group C=2.0-2.9 mg/L;
Group D=3.0-3.9 mg/L;
Group E>3.9 mg/L.

Urine Fluoride Levels:

High F village=3.47+1.95 mg/L
Low F village=1.11+0.39 mg/L

Confounding Factors:

(1) The two villages have similar urine iodine levels (p>0.3), and blood lead levels (p>0.48). (2) Neither village has fluoride pollution from burning coal or other industrial sources. (3) None of the residents reported drinking brick tea. (4) Children who had been absent from either village for 2 years or longer, or who had a history of brain disease or head injury were excluded from study.

Type of IQ Test

CRT-RC (Combined Raven’s Test for Rural China)

Results:

(A) Mean IQ of high F village (92.02+13.00) is lower than low F village (100.41+13.21), p<0.01. (B) Higher drinking water F is significantly associated with higher rates of mental retardation (IQ<70) and borderline intelligence (IQ=70-79), p<0.05. (C) Children’s IQs are not related to urinary iodine, family income, or parent’s education level.

Conclusion:

“In endemic fluorosis areas, drinking water fluoride levels greater than 1.0 mg/L may adversely affect the development of children’s intelligence.”

Li Y, et al. (2003). Effects of endemic fluoride poisoning on the intellectual development of children in Baotou. Chinese Journal of Public Health Management 19(4):337-338 (republished in Fluoride 2008; 41:161-64).

Location of study:

Baotou, Inner Mongolia, China

Size of study:

936 children (720 children from high-F endemic area; 236 children from low-F control area)

Age of Subjects:

6-13 years old

Source of F exposure:

Water

Fluoride exposure levels:

“The region classified as endemic was designated using the 1981 standards for designation of endemic regions laid out in 1981’s Standards for Endemic Fluorosis Prevention and Treatment Work”

Type of IQ Test

Illustrated version of the Chinese Standardized Raven Test for children in rural areas

Results:

(A) Average IQ of children in endemic area (92.07) somewhat lower than that of control area (93.78), NS. (B) Rate of children with low IQ (<69) greater in endemic area (10.38%) than in control area (4.24%) (“high statistical significance”, but no p value given).

Conclusion:

“In our study, we found that the average IQ of children in a fluoride endemic area was somewhat lower than the control, but the result was not statistically significant (p > 0.05). The percentage of children with fluorosis, however, was higher as compared to the control, and this was very significant statistically.”

(A) Significantly lower operation score on IQ test in high F area (48-54) versus low F area (52-59), p < 0.01. (B) Lower total IQ score in high F area (78-100, average) than in low F area (109-118, average-high), although not statistically significant (C) High F subjects have significantly lower scores on several of the performance tests (speech fluency, recognition, similarity, p < 0.01, and digit span, p < 0.05), and this correlates with elevated levels of oxidative stress.

Conclusion:

“The results suggest that some cognitive function limitations exist in those suffering from chronic fluoride poisoning, and its biologic basis may be related to the levels of SOD and NO [indices of oxidative stress].”

(A) Average IQ is lower in High-F area than in Low-F area (76.67+7.75 vs. 81.67+11.97), although the difference does not reach statistical significance. (B) The rate of extremely low and borderline IQ is higher in the High F areas than in the Low F areas (16.67% vs. 10% and 36.67% vs. 16.67, respectively), although these differencese do not reach statistical significance.

Conclusion:

“High iodine and high fluorine have certain influence on children’s intelligence and thyroid function.”

(A) Average IQ of High F/Low I group (68.38+19.12) and Low F/Low I group (75.53+6.92) is lower than control group (82.79+8.98), p<0.01. (B) IQ of High F/Low I group is lower than Low F/Low I group, p<0.01. (C) Significant interaction exists between High Fluoride and Low Iodine, p<0.01. (D) IQ ranking of high F groups show significant deficits compared to control, p<0.01.

Conclusion:

“The IQ results of this study show no significant difference between the average IQs of those children from the high fluoride only areas and the high fluoride/high iodine areas, however the result from the high fluoride/low iodine group show statistically significant differences as compared to that of the low fluoride/low iodine group. In short, it appears that the presence or lack of iodine is a more significant factor in both the prevalence of goiter and average IQ.”

118 children (60 children in High-F village; 58 children in Low-F village)

Age of Subjects:

10-12 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

– High F village = 3.15+0.61 mg/L – Low F village = 0.37+0.04 mg/L

Urine Fluoride Levels:

– High F village = 4.99+2.57 mg/L – Low F village = 1.43+0.64 mg/L

Confounding Factors:

(1) Children included in the study are lifelong residents of study area. (2) Villages have similar population size, social, economic and educational backgrounds. (3) Children with congenital or acquired neurological disorders were excluded.

Type of IQ Test

Chinese Combined Raven’s Test, Copyright 2 (CRT-C2)

Results:

(A) Average IQ of children from High F village (92.27+20.45) is lower than children from Low F village (103.05+13.86), p<0.005. (B) More “retarded” (IQ=<70) and “borderline” intelligence (IQ=70-79) children in high F group (21.6%) than in low F group (3.4%), p<0.005. (C) Significant inverse relationship exists between urinary F and IQ.

Conclusion:

“The findings of this study thus replicate those of earlier studies and suggest that a real relationship exists between fluoride exposure and intelligence.”

Zhang J, et al. (1998). The effect of high levels of arsenic and fluoride on the development of children’s intelligence. Chinese Journal of Public Health 17(2):119.

Location of Study:

Kuitun region, Urumqi, China

Size of Study:

164 children

Age of Subjects:

4-10 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

For the 4 to 8 year olds, the fluoride level their entire life (including during fetal development) was between 0.49 and 0.81 ppm. The 9 year olds were exposed to high fluoride (level not provided) during fetal development. The 10 year olds were exposed to high fluoride during fetal development and their first year of life.

Type of IQ Test:

50-point evaluation tests created by Japanese researcher, Shigeo Kobayashi

Results:

No difference in IQ among the 4 to 8 year olds, a slight (non-significant) reduction in IQ among the 9 year olds (who were exposed to fluoride during fetal development), and a significant reduction among the 10 year olds (who were exposed during fetal development and their first year of life).

Conclusion:

“Even though there were differences in the results from the 10 year-old subjects from the normal comparative group, in contrast to subjects from the high fluoride high arsenic group and the high fluoride group, these results might not be overtly representative as less number of subjects from the high fluoride group has been tested.”

Yao Y, et al. (1997). Comparative assessment of the physical and mental development of children in endemic fluorosis area with water improvement and without water improvement. Literature and Information on Preventive Medicine 3(1):42-43.

Location of study:

Chaoyang City, Liaoning Province, China

Size of study:

823 children (326 children from fluorosis area with water improvement; 183 children from fluorosis area without water improvement; 314 children from non-fluorosis area)

Age of Subjects:

7-14 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

– Fluorosis area without water improvements = 2.0 mg/L- Fluorosis with water improvements = 0.33 mg/L (prior to improvement 8 years before study, the F level was 2.0 mg/L)- Non-fluorosis area = 0.4 mg/L

Confounding Factors:

– All children born locally.

– Areas in study have adequate iodine exposure and similar levels of economic development, living conditions, school size, and number of teachers.

Type of IQ Test

CRT-RC (Combined Raven’s Test for Rural China)

Results:

(A) Children in fluorosis area (without water improvement) have lower average IQ than children in fluorosis area (with water improvement) for all age groups, p<0.01. (B) Children in fluorosis area without water improvement have lower average IQ than children in non-fluorosis area for all age groups, p<0.01. (C) Children born prior to water improvement program in fluorosis area with water improvement have lower average IQ than children in non-fluorosis area, p<0.05. (D) No significant difference in intelligence exists between children born after water improvement and children in non-fluorosis area.

Conclusion:

“These results show that water improvement and defluoridation can improve the mental and physical development of children in a fluorosis area.“

Yao Y, et al. (1996). Analysis on TSH and intelligence level of children with dental Fluorosis in a high fluoride area. Literature and Information on Preventive Medicine 2(1):26-27.

Location of study:

Chaoyang City, Liaoning Province, China

Size of study:

536 children (78 children from high-fluorosis area; 188 children from light-fluorosis area; 270 children from non-fluorosis area)

Age of Subjects:

8-12 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High-F area: <11 mg/L Low-F area: 2.0 mg/L Control area: 1.0 mg/L

Confounding Factors:

(1) Children in each of the three areas have adequate iodine exposure as determined through urine analysis. (2) The three areas have similar economic development, schools, and teachers.

Type of IQ Test

Raven test—Associative Atlas (Version of Chinese village)

Results:

(A) Average IQ of children with dental fluorosis in high-fluorosis area and light-fluorosis areas is lower than children in non-fluorosis area, p<0.01. (B) Average IQ of children with dental fluorosis from high-fluorosis area is lower than those from light-fluorosis area, p<0.05. (C) Rate of high IQ (>120) is lower in high-fluorosis area (3.85%) and light-fluorosis area group (6.91%) than non-fluorosis area (10.74%) (no p value given).

Conclusion:

“The results of the intelligence tests show that a high level of fluoride influences children’s IQ, which is consistent with some previous data. It is worth mentioning that the higher the degree of dental fluorosis, the more negative the impact on the children’s intelligence level. This is an issue which merits utmost attention.”

320 children (160 children from high-F village; 160 children from lower-F village)

Age of Subjects:

7-14 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High-F village = 4.12 mg/L Lower-F village = 0.91 mg/L

Confounding Factors:

(1) Similar occupations, living standards, and social customs in the two villages. (2) Only children whose mothers lived in the village during pregnancy were included in study. (3) Parents’ educational level was determined (and found to have a significant influence on IQ, p < 0.01).

Type of IQ Test

“Official intelligence quotient (IQ) tests lasting 40 minutes”

Results:

Children in High-F village have significantly lower average IQ (97.69+13.00) than children in lower-F village (105.21+14.99), p<0.01.

Conclusion:

“The results of this study indicate that intake of high-fluoride drinking water from before birth has a significant deleterious influence on children’s IQ in one of two similar villages.”

(1) Children were excluded from study if they had a low intellectual ability due to genetic inheritance, past illness, malnutrition, uses of medication, or other reasons. (2) “Significantly greater” percentage of children with below average head circumference in High F area (18.37%) than in Control area (9.64%) (no p value given).

Type of IQ Test

Wechler Preschool and Primary Scale of Intelligence (WPPSI)

Results:

(A) Average Total IQ in High F group (95.64+14.34) is lower than in control group (101.23+15.84), p<0.05. (B) Average Performance IQ in High F group (94.33+14.76) is lower than in Control group (101.77+18.12), p<0.01. (C) Average Verbal IQ is not significantly different. (D) In High F area, children with below-normal head circumference have lower average IQ (89.07+15.69) than those with normal head circumference (97.13+8.06), p<0.01.

Conclusion

“The results show that a high fluoride intake has a clear influence on the IQ of preschool children, manifesting itself primarily as damage to performance intelligence.”

Average IQ of workers with industrial fluorosis was significantly lower (68 to 72) than fluoride-exposed workers without industrial fluorosis (84.5), and IQ of fluoride-exposed workers without fluorosis (84.5) was significantly lower than IQ of non-exposed workers (99.4).

Conclusion:

“it may be determined that industrial fluorine poisoning has gradually progressive effects on the normal function and metabolism of the adult brain and other aspects of the nervous system. With the progression of the course of fluorosis, neurological damage gradually worsens, with the degree of damage closely related to the length of exposure to fluorine, nail fluorine content, and other factors. Damage from high concentrations of fluorine not only affects bones and ligaments, tendons, and other soft tissue, but is also quite widespread throughout the entire nervous system. This is of major significance for worker protection and other areas.”

(1) Water iodine level used as variable. (2) Child’s pre-school education history was determined. (3) Parent’s literacy was determined.

Type of IQ Test

Bient-Siman

Results:

(A) Children in areas with high-fluoride and low-iodine have significantly lower IQs than children in areas with high-fluoride and high-iodine, p < 0.01. (B) More children have low IQ (< 69) in areas with High F/High I (10.53%), High F only (7.32%), and High F/Low I (12.82%) than in control group (1.61%)

Conclusion:

“The number of children whose level of intelligence is lower is significantly increased in regions of high fluoride/iodine, regions of high fluoride only, regions of high fluoride/low iodine, against their respective comparative groups. . . . This could be demonstrative of the fact that fluoride acts to increase the toxicity and worsen the occurrence of thyroid swelling.”

(1) The areas have similar levels of fluoride in water (0.3 mg/L) and air (0.02-0.51 mg/m3) and similar levels of zinc in soil. (2) The areas townships have similar economic and cultural status, lifestyle, dietary habits, basic constituents of food. (3) Age, gender, and grade level of the children are kept “as constant as possible.” (4) Children with acute or chronic diseases not related to fluoride were excluded from study.

(A) Children with dental fluorosis in mid-exposure group (HiF2) have reduced short-term mental capacity (p<0.05), reduced mental capacity index (p < 0.01), and reduced NLF scores (p<0.01) as compared to children with no fluorosis and children with lower exposure.(B) Children with dental fluorosis in high-exposure group (HiF3) have reduced short-term mental capacity (p<0.01), reduced mental capacity index (p < 0.01), and reduced NLF scores (p<0.01) as compared children with no fluorosis and children with low exposure.

Conclusion:

“As shown in this study, the mental work capacity (MWC) of the two groups of children with grade 3 dental fluorosis was lower than the two groups with no dental fluorosis. . . . This indicates that early, long-term exposure to excess fluoride causes deficits in memory, attention, and reaction time, but 12–13 year-old children with only recent exposure show no major effects. Studies [on human fetuses] have already shown that the developing brain is one of the ripest targets for disruption by fluoride poisoning. Given that before six years of age the human brain is in its fastest stage of development, and that around seven and eight basic structural development is completed, therefore the brain is most vulnerable to damage from excess fluoride intake before this age.”

Yang Y, et al. (1994). The effects of high levels of fluoride and iodine on intellectual ability and the metabolism of fluoride and iodine. Chinese Journal of Epidemiology 15(4):296-98 (republished in Fluoride 2008; 41:336-339).

Location of study:

Shandong Province, China

Size of study:

60 children (30 from high-F village, 30 from Low-F village)

Age of Subjects:

8-14 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High F/High Iodine area = 2.97 mg/L Control area = 0.5 mg/L

Urine Fluoride Levels:

High F/High Iodine area = 2.08+1.03 mg/L Control area = 0.82+0.56 mg/L

Type of IQ Test

Chinese Comparative Scale of Intelligence Test

Results:

(A) Children in high F/high iodine area have lower IQ (76.67+7.75) than those in low F area (81.67+11.97), although the difference is not statistically significant.(B) Greater percentage of children have moderately low IQ (<79) in High F/High Iodine area (76.67%) than in control area (36.67%), p<0.01.

Conclusion:

“An excess of fluoride and a lack of iodine in the same environment has been shown to have a marked effect on child intellectual development, causing a more significant intellectual deficit than lack of iodine alone.”

242 children (121 children from high-F villages and 121 children from the low-F villages)

Age of Subjects:

7-16 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High-F villages = 2.1+7.6 mg/L Control villages = 0.6+1.0 mg/L

Confounding Factors:

(1) Dental fluorosis rates were determined in both areas (90.9% in High-F area vs. 21.5% in Low-F area). (B) Both areas are in the countryside, are 15 km from each other, and share the same Han ethnicity. (C) The geography, culture, education, living standard, and social economic conditions are “very similar.”

IQ Test:

Wechsler Intelligence Scale for Children

Results:

(A) Children in the High-F villages have significantly lower IQs at each age group studied: 7-10 (p < 0.02); 11-13 (p < 0.01); 14-16 (p < 0.03); 7-16 (p < 0.01). (B) Significantly more children in High-F villages have “critical state” IQ, p < 0.01. (C) When children within the High-F villages are stratified into highest-F (5.2-7.6 mg/L), and lowest-F levels (2.1-3.2 mg/L), the children in the higher-F areas had significantly lower IQ than the lower-F areas (p < 0.05).

Conclusion

“The results show that the level of intelligence of primary and secondary students from the high fluoride area and that of primary and secondary students from the non-high fluoride area had very significant differences, proving that high fluoride has adverse effects on the mental development of students. The higher the water fluoride is, the lower the level of IQ.”

Guo X, et al. (1991). A preliminary investigation of the IQs of 7-13 year old children from an area with coal burning-related fluoride poisoning. Chinese Journal of Endemiology 10(2):98-100 (republished in Fluoride 2008; 41(2):125–28).

Location of study:

Xinshao County, Hunan Province, China

Size of study:

121 children (60 children with mild to severe fluorosis from an endemic area where coal is used as a fuel source; 61 children from a non-endemic area where wood is used as a fuel source)

The two areas are neighboring townships with “very similar” economies, cultures, living standards, lifestyles, public health, and education.

IQ Test:

Chinese Binet IQ Test

Results:

(A) Children from endemic fluorosis area have lower average IQ (76.7) than children in non-endemic area (81.4), p<0.05. (B) A greater percentage (30%) of children in endemic area have low IQ (<69) than in non-endemic area (11.5%), p<0.05.

Conclusion:

“In summary, although diminished intellectual ability can result from a multitude of factors (both innate and acquired) that influence neural development and cell division in the cerebrum, the comparison conducted in this study of two areas where the other environment factors are basically the same shows clear differences in IQ, and it [is] probable that this difference is due to a high fluoride environment.”

Chen YX, et al. (1991). Research on the intellectual development of children in high fluoride areas. Chinese Journal of Control of Endemic Diseases 6(Suppl):99-100 (republished in Fluoride 2008; 41:120–24).

Location of study:

Linyi County, Shanxi Province, China

Size of study:

640 children (320 children from High-F village; 320 children from Lower-F village)

Age of Subjects:

7 to 14 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High-F village = 4.55 mg/L Lower-F village = 0.89 mg/L

Confounding Factors:

The occupations, culture, standard of living, lifestyle habits, access to health and transportation facilities are “essentially the same” between the two areas.

IQ Test:

Rural version of Chinese Standardized Raven Test

Results:

Average IQ of children in High-F village (100.24+14.52) significantly lower than children in lower-F village (104.03+14.96), p<0.01.

Conclusion:

“The results of this study indicate that there is significant difference between the intellectual ability of the 7–14 year old children from the [fluorosis] endemic area and those of the control, and moreover that the average IQ of the children from the endemic area is clearly lower.”

Children from endemic fluorosis area had lower IQ than those from non-endemic area at all ages except <7 (p < 0.05)

Excerpt:

“From these results, it can be concluded that excessive consumption of fluorine and aluminum in the early stage of development directly impacts the development of the human brain, which causes the delayed intellectual development seen in children living in the endemic areas.”

Qin LS, Cui SY. (1990). Using the Raven’s standard progressive matrices to determine the effects of the level of fluoride in drinking water on the intellectual ability of school-age children. Chinese Journal of the Control of Endemic Diseases 5(4):203-04 (republished in Fluoride 2008; 41:115–19).

Location of study:

Jing County, Hubei Province, China

Size of study:

447 children (141 children from High-F area; 159 children from “normal” F area; 147 children from low-F area)

Age of Subjects:

9 to 10.5 years old

Source of Fluoride Exposure:

Water

Water Fluoride Levels:

High F = 2.1-4.0 mg/L“Normal” F = 0.5-1.0 mg/LLow F = 0.1-0.2 mg/L

Confounding factors:

All children had grown up drinking well water in their home village.

IQ Test:

Raven’s Standard Progressive Matrices

Results:

Children in High F (21.17%) and Low F (23.03%) areas had lower average IQ scores than children in normal F area (28.14%), p<0.01.

Conclusion:

“All of these finding serve to indicate that both high and low fluoride can affect the normal development and function of the cerebrum as well as the entire nervous system causing a decrease in intellectual ability.”

Ren D, et al. (1989). A study of the intellectual ability of 8-14 year-old children in high fluoride, low iodine areas. Chinese Journal of Control of Endemic Diseases 4(4):251 (republished in Fluoride 2008; 41:319-20).

Location of study:

Shandong Province, China

Size of study:

329 children (160 children in High F/low Iodine area: 169 children in Low-F/Low Iodine area)

Age of Subjects:

8 to 14 years old

Source of Fluoride Exposure:

Water

Fluoride exposure levels:

N/A

Confounding factors:

Both study groups had low iodine intake.

IQ Test:

Wechsler Intelligence Test

Results:

– Average IQ of children in the High Fluoride/Low Iodine group (IQ=64.8) significantly lower than the children in the Low Fluoride/Low Iodine group (IQ = 85.0), p<0.01.- The percentage of children with low IQ (<69) significantly greater in High F/Low Iodine group (40.6%) than in Low Fluoride/Low Iodine group (13.6%), p<0.01.

Conclusion:

“From the results it is evident that disrupted child intellectual development is among the effects on the human body from a harmful environment containing both high fluoride and low iodine, and this disruption is clearly much more serious than the effects of iodine deficiency alone.”